Specific digestion procedure and apparatus for use in the production of chemical wood pulp



Feb. 17, E931. c. E. PETERSON 3 SPECIFIC DIGESTION PROCEDURE AND APPARATUS FOR USE IN THE PRODUCTION OF CHEMICAL WOOD PULP Filed Aug. 12, 1929 2 Sheet t 1 [II a "475%,, V 5 flan/fa t i T Z 12 kil T M a e). 17, 1931. c. E, PETERSON 1,792,703

SPECIFIC DIGESTION PROCEDURE AND APPARATUS FOR USE IN THE PRODUCTION OF CHEMICAL WOOD PULP Filed Aug. 12, 192.9 2 Sheets-Sheet 2 90 120 7/me 1 Mina/es Patented Feb, 17, 19%

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GLIFFOED E. PETEBEOH, ASEEYILLE, NORTH CAROLINA, ASSIGNOB TO THE. CHAM- PION rmnn COMPANY, OF CANTON, NORTH GARPLINA, A CORPORATION OF OHIO SPECIFIC DIGESTION PROCEDURE AND APPTUS FOR USE IN IROQU'GTION 0F GHEMIG'AL WOOD PULP I Application filed August 12, 1929. smart. 385,370.

This, invention relates to processes for the preparation of chemical fibrous pulps adapted for paper making, and is concerned with an improvement in the digestion procedure for the production of such pulps.

In United States application Serial No. 386,225, filed August 15, 1929, in the name of George M. Trostel, there is described a di-,

gestion process which involves digesting wood in a cooking liquor, containing caustic soda and sodium sulfid, characterized as follows: -The liquor -contains (total) active chemical in an amount from about to about grams per liter, the quantity of active chemical present,with respect to wood,- being from about 28 to about 36 pounds for each 100 pounds of wood undergoing the digestion treatment. The weights and proportions of chemicals above and hereinafter set 'out are expressed as of equivalent sodium carbonate.

As will be appreciated, a practical result of the carrying out of the above-described digestion process is a relatively high dilution of cooking liquor, with consequent use of a larger volume of the same per unit weight of wood chips ordinarily employed as a in anyevent, is more nearly completely filled than therefore. By virtue of this increase in mass, it has been found that circulation ofthe liquor (i. e., one complete movement of the body of liquorthrough the customary outside indirect heating means and return to the body of liquor) is considerably slowed down,-f'or instance, from the 6 to 12 minute periodofthe old practice to as long as a 60 to 70 minute period according to the practice of the said improved digestion procedure.

As a consequence, I have found that the upper portion of the chip-content of the digester will have been raised to cooking temperature as much as one hour before the bottommost portion of the chip-content has been brought to the said temperature, and that the ensuing digestion is uneven and results either in under-cooking the. lower portion of the chips or else in an equally disadvantageous over-cooking of the upper portion of the chips.

An object of the present invention is to provide 'a method of bringing the tempera ture of the whole digestion mass'uniformly to cooking temperature, whereby to avoid unevenness of digestion throughout the same. The above, and other, objects of the invention are attained by initially heating the mass,while carrying out the outside circulation of liquor from bottom to top of the digester contents,-by means of steam directly introduced into the said contents at a plu rality of points near the bottom of the mass. In so operating, I preferably omit the step of indirect heating of the circulated liquor during the initial operation of raising the temperature of the mass to cooking temperature. After the mass has been brought to cooking temperature, I may, and preferably do, discontinue the direct addition of steam to the digester contents,.and thereafter maintain the same at said temperature by recourse to indirect heating of the circulated liquid.

I have found that, by operating in accordance with the procedure forming the basis of the present invention, all parts of the digester contents are brought to the desired elevated temperature at substantially the same time, and that thereby the resulting cook is uniform throughout the mass. The directly added steam serves to impart heat both to the liquor (as the same is about to be withdrawn from the bottom of the digester and reintroduced at the top thereof) and'upward'ly to the solids retained in the digester.

The invention will be further understood from the following specific description of a preferred embodiment thereof in connection with the accompanying drawings in which:

Fig. 1 illustrates in side elevation a preferred arrangement of ap aratus for carrying into effect the process of the present invention; and

Fig. 2 is a graphic representation of the improvement in uniformity of heating affected by operating in accordance with the present invention over the practice theretofore commen.

In F i 1, 1 is a digester of known type provide near its base with a false bottom :2, 2. 3 represents a conventional man-hole" closure, and at a conventional means for drawing oil digester contents. The system represented b valved conduits 5, 5, 5, pump 6, means for indirect heating 7, and valved inlet 11, is a conventional system for the circulation of liquid from beneath false bottom .2, 2 to top 8 of digester 1.- To this conventional apparatus 1 have added the valved by-pass conduit 12 for circulation of liquid past the heating means 7, and a plurality of perforated steam pipes 9, 9 for the introduction of direct steam into the digester mass at the base thereof from any source of direct steam 10, 10.

In operation, after the digester 1 has been charged'with the requisite amount of wood chips and cooking liquor, valved inlet 11 is closed, valved by-pass conduit 12 is opened, and direct steam is admitted to the mass from source 10, 10 through a plurality of pipes 9, 9 provided for so much of their length as is located within the digester with many perforations. Meanwhile, circulation of liquid through the system 5, 6, 12, 5 is maintained.

As soon as the temperature of the digester contents has been raised to cooking temperature, the addition of direct steam at 9, 9 is discontinued, valved by-pass conduit 12 is closed, valved inlet 11 is opened, and the temperature oi the liquor is maintained by the indirect heating of the circulated liquor in device 7.

In the graph of Fig. 2, A, A A are curves representing the course of the heatin at top, middle, and bottom, respectively, oft e mass, when operating in accordance with the process of the present invention, and B, B 13 are curves representing the course of the heating at top, middle, and bottom, respectively, of the mass, when operating in accordance with old practice.

In the above, reference has been had to initially charging the digester with the requisite amount of cooking liquor. By this I refer to the obvious fact that the addition of water in the form of steam during the heat ing-up stage of necessity results in a certain determinable dilution of the cooking liquor, and to the corollary fact'that, to provide for such dilution, the concentration of the liquor initially added must be correspondingly higher so that the liquor, when heated to the cooking temperature, will have the aforesaid characteristics as to concentration. Therefore, when reference is had, in the foregoing description and in the appended claims, to a liquor having a concentration of active chemical in an amount from about to about grams per liter, 1 mean to define menace thereby the concentration-characteristic of the cooking liquor after the same has been diluted by addition of the necessary steam. It involves merely an engineering calculation to determine the amount of steam of a certain temperature necessary to raise the temperature of a definite-amount of a specific body of liquor and wood chips from an initial temperature to the required cooking temperature, and hence the proper initial concentration of the liquor prior to the dilution.

I claim:

1. In a process for the production of pulp involving the digestion of wood chips in a relatively dilute alkaline cooking liquor by a procedure having as an essential element the continuous withdrawal of liquor (from the bottom of a body of liquor and chips and the continuous addition of the withdrawn liquor to the said body at the top thereof, the steps which consist in raising the temperature of said body to desired cooking temperature by introduction of direct steam into said body near the bottom thereof, and thereafter maintaining the said cooking temperature by indirect heating of the circulated liquor.

2. In a process for the production of easybleaching sulfate pulp involving the digestion of chips of coniferous wood of relatively high resin content in a caustic soda and sodium sulfidecontaining cooking liquor containing active chemical in an amount from about 70 to about 80 grams per liter, the quantit of active chemical present in said liquor being from about 28 to about 36 ounds for each pounds of Wood treated y a procedure having as anessential element the continuous withdrawal of liquor from the bottom of a body of liquor and chips and the continuous addition of the Withdrawn liquor to the said body at the top thereof, the steps which consist in raising the temperature of said body to desired cooking temperature by introduction of direct steam into said body near the bottom thereof, and thereafter maintaining the said cooking temperature by indirect heating of the circulated liquor, the initial concentration of said liquor being so adjusted that the subsequent dilution by means of the added steam yields at cooking temperature a cooking liquor of the aforesaid concentration.

Tn testimony whereof, I affix my signature.

CLIFFORD E. PETERSON. 

